This invention relates to an improved position-measuring technology sing diffused light, and particularly to a method and a system for determining the reference position to accurately locate components in placement apparatus such as chip mounters.
There is a considerable demand for devices that are capable of mounting or positioning small components such as integrated circuits, resistors, capacitors and the like at accurate locations on substrates such as printed circuit boards. This type of apparatus is generally referred to as a "chip" or "surface" mounter.
The components that are positioned are generally fed to the apparatus at a feeder location. Frequently, the components are positioned in specially-formed tapes that form individual pockets in which the components are received. Tape feeders present these components to a pick-up device which then picks them up and positions them on the substrate.
At one time, these components were accurately positioned on the pick-up apparatus by gripping fingers or other devices that physically engaged the component and would shift the component to a corrected position before placement. Many types of components do not, however, lend themselves to handling in this manner.
Therefore, a wide variety of types of non-contact sensors have been employed. These sensors sense the actual position of the component as picked up by the pick-up device. By being able to determine the actual position of the component, then correction in its position can be made when the component is positioned on the substrate.
This invention deals primarily with such a non-contact type of sensing arrangement and method. One type of arrangement which is conventionally utilized for providing this sensing utilizes a plurality of laser-type light sources that operate through optical devices to cast a plurality of parallel light rays across a sensing station in which the component and its pick-up device is positioned. A receptor is disposed on the other side of the pick-up device and component being held and a shadow is cast on that receptor. By rotating the component in the path of the light rays it is possible to measure the actual position of the component from the shift of the shadow and its size. These types of devices can be quite accurate.
In systems wherein diffused light is used, since diffused light can directly be used, optical devices such as lenses to emit parallel lights can be omitted. In the systems using diffused light, the position of a shadow cast oil a receptor is measured and determined with reference to the reference position or reference orientation. Thus, if the positional relationship of the receptor, the light source, and the pick-up nozzle deviates from the theoretical or designed positional relationship, accuracy of determination of orientation of a component will be significantly decreased. For example, if the position of the pick-up nozzle is slightly shifted toward either the receptor or the light source, the position of the shadow cast on the receptor will be significantly affected because the light emitted from the light source diffuses. Further, distortion is like to occur in each part of the apparatus with time, resulting in a decrease in accuracy. Accordingly, it is difficult to maintain high performance.
A principal object of this invention is to provide a method for accurately determining the reference position to improve accuracy of determination of the component's orientation.